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The World Health Organization (WHO) classification of tumors of hematopoietic and lymphoid tissues (2001) defined a provisional entity named refractory anemia with ringed sideroblasts associated to marked thrombocytosis (RARS-MT). Diagnosis of RARS-MT requires more than 15% of ringed sideroblasts in bone marrow aspirate and the existence of a thrombocytosis in blood, with a platelet count above 600 x 10(9)/L. Nevertheless, controversy exists regarding this platelet count "cut-off" value and, when RARS-MT was defined, the JAK2 mutation and its importance in the study of myeloproliferative disorders was unknown. We present the results of a Spanish retrospective multicentric study, which includes 76 cases of RARS with associated thrombocytosis (platelet count above 400 x 10(9)/L) at diagnosis (RARS-T), 36 of them with a platelet count above 600 x 10(9)/L. Our aim was to analyze their clinical, analytical and morphological characteristics, and to establish correlations with the JAK2 mutational status.

To analyze the usefulness of bone marrow (BM) study in the diagnosis of fever of unknown origin (FUO) in patients infected by the human immunodeficiency virus (HIV) in a single center during a period of 42 months.182 episodes of FUO in 162 patients p3th HIV infection were studied. Age, sex, risk factor for HIV infection, hemoglobin level, counts of leucocytes, neutrophils, lymphocytes, CD4 positive lymphocytes, platelets and levels of hepatic enzymes, albumin and beta 2-microglobulin were studied. BM aspirate was performed in all episodes for cytologic and microbiologic examination, and BM biopsy was done in 43. Analysis of factors related with the probability of diagnosis by BM examination was carried out.The median age was 33 years (range, 22-70), and 123 were males. Drug abuse was the most frequent risk factor for HIV infection (63%). One hundred thirty patients had previous AIDS diagnosis before they were evaluated for unexplained fever. A specific diagnosis was achieved in 161 episodes (88%) and the most frequent diagnoses were Mycobacterium spp. (55%) and Leishmania spp. (14%) infections. Fifty-four episodes (30%) were diagnosed by BM examination, and in 36 (20%) BM study was the only diagnostic tool. Examination of the BM aspirate yielded the diagnosis in 40 out of the 178 episodes (13%), whereas BM biopsy was a diagnostic tool in 8 (19%); in 9 additional cases (21%) granulomas were observed. Microbiologic study of BM smears for mycobacterial infections was positive in 28 of the 143 episodes (19%), and the culture for Leishmania was positive in 2 out of the 42 cases. The presence of thrombocytopenia (75 x 10(9)/l) and elevated serum levels of aspartate-aminotransferase (AST) (100 U/l) were the factors associated with a high probability to obtain the diagnosis through BM study.In patients infected by the HIV and unexplained fever, BM examination is an useful procedure for the diagnosis, particularly in areas where infections by Mycobacterium spp. and Leishmania are prevalent. So that, in our setting, systematic use of this procedure is justified for diagnosis of FUO in those patients.